|Opposition leaders in Bahrain say the crackdown against Shia protesters is a campaign of 'terror' against citizens [EPA]
Bahrain has stepped up the arrests of Shia Muslims, including many cyber activists, with more than 300 detained and dozens missing since it launched a crackdown on pro-democracy protests, the opposition has said.
Activists and politicians said on Thursday that a growing number of reform campaigners are going into hiding, after the country's most prominent blogger was arrested on Wednesday.
"The situation is critical ... Almost all the bloggers and activists who aren't in jail are now in hiding," Nabeel Rajab, head of the Bahrain Centre for Human Rights, said.
Earlier this month, the Gulf Arab island's Sunni rulers imposed martial law and called in troops from fellow Sunni-ruled neighbours, including Saudi Arabia, to quell the protest movement led mostly by the state's Shia majority.
The severity of the crackdown, in which public gatherings are banned and security forces have been deployed at checkpoints, stunned Bahrain's Shia Muslims and angered the region's non-Arab Shia power Iran.
Saudi Arabia and other Gulf Arab states fearful of rising Iranian influence see Bahrain as a red line among the popular uprisings that have swept the region since January.
"The government says it is taking steps to ensure stability and security, but what's happening is the exact opposite," Mattar Ibrahim Mattar, a member of the country's largest Shia opposition group Wefaq, said.
"We're in one of the most dangerous stages, where citizens have no security. They're being arrested and kidnapped at checkpoints that are all over Bahrain. The checkpoints are a place of fear."
Mattar said Wefaq had counted 302 arrests on Wednesday but believed the number would soon reach 400.
Meanwhile, the Lebanese Shia movement Hezbollah denied on Thursday that it had given military training to Shia Bahraini protesters.
Sheikh Khaled bin Ahmed Al Khalifa, Bahrain's foreign minister, said in an interview with the pan-Arab Al Hayat newspaper on Wednesday that Hezbollah, which he described as a terrorist organisation, had trained Bahraini "elements" in Lebanon.
In a recent televised speech, Sayyed Hassan Nasrallah, the Hezbollah leader, offered support to the protesters in Bahrain, but did not specify what kind of help.
Last week, Bahrain lodged a formal complaint to the Lebanese government over Hezbollah's offer.
"We have to affirm that our Bahraini brothers did not ask us for any military or security training on any day and we have not given any training of that kind," Hezbollah said in a statement, adding that the group had only provided political and moral support for the protests.
Bahraini activists and opposition politicians said the campaign of arrests had taken a chilling turn following the arrest of the prominent blogger Mahmood al-Yousif, who was released from custody on Thursday evening.
"Thank you ALL for your support of both myself and @Redbelt. We are now safe and sound at home. Taken in. Investigated. All ok. Released," al-Yousif wrote via Twitter.
Al-Yousif, 50, blogs in English. His arrest was seen as a further step in Bahrain's crackdown on anti-government protests sweeping the country.
Yousif is considered a liberal who had criticised the Sunni rulers for their lack of reform but had also chided Wefaq for not moving more quickly to talks with the government.
More than 60 per cent of Bahrainis are Shia and most want a constitutional monarchy.
Demands by hardliners for the overthrow of the monarchy have alarmed minority Sunnis.